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FIELD OBSERVATION REPORT
September 23-25, 2014
Lido Key Hurricane and Storm Damage Reduction Project
Benthic Resource Investigation
Lido Key, Sarasota County, Florida
153076.03
Katy Brown (biologist), Judd French (field support), Ben Alcocer
(field support), and Scott Tillman (captain)
CB&I completed a benthic resource investigation in support of the Lido Key Hurricane and
Storm Damage Reduction Project from September 23-25, 2014. The project is anticipated to be
constructed in 2015 and includes beach nourishment and construction of three (3) groins. This
investigation was required in order to locate seagrass and/or hardbottom resources that may be
present in the footprint of the beach fill and groin placement areas and the proposed water quality
mixing zones for the beach fill and the Big Sarasota Pass borrow areas. Results from this report
will be used in support of obtaining the Florida Department of Environmental Protection (FDEP)
permit and consultation with NOAA National Marine Fisheries Service (NMFS) Habitat
Conservation Division (HCD). Aubree Hershorin (USACE) and Mark Sramek (NMFS HCD)
joined the CB&I crew on September 23 to observe and participate in the resource survey.
METHODS
The initial phase of this investigation involved reviewing existing data, including sidescan sonar
survey data provided by the USACE, in-house aerial photographs, and previous Lido Key in situ
resource investigations (CPE, 1992; Dial Cordy, 2001). These recent and historical data were
used to determine areas of potential seagrass and hardbottom resources and to plan field
investigation sites. Figure 1 shows the location of the overall investigation area, the specific
investigation methodologies conducted and the sidescan contacts (areas that warranted
investigation). To efficiently investigate the large survey area, a combination of methods was
employed, including towed video, towboard diver surveys and diver verification.
First, a DGPS-integrated towed video camera method was used to survey the borrow areas in Big
Sarasota Pass and the nearshore fill placement area to locate potential benthic resources. This
method allowed for the collection of data over a large area. The camera was deployed from the
vessel and the streaming video was viewed by a biologist topside in real-time. When potential
seagrass or hardbottom was observed, a fix was taken in Hypack navigational software to mark
the location of the resource. The position data was also recorded and displayed as GPS
coordinates overlaid on the video. The preliminary survey lines were spaced 500 ft apart;
however, if resources were observed, then the spacing was systematically decreased to delineate
the resource area. Cross lines (e.g., C1) were also run to determine the outer extent of resources.
Towed video survey lines were concluded once the investigation area boundary was reached or
when the water depth became too shallow (less than 1 m [3 ft]) for the vessel to operate.
When general conditions allowed, the towboard survey method was used. This method allowed
biologists to directly assess areas of potential seagrass inside Big Sarasota Pass. This method
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involved two snorkelers being towed astern of the vessel at slow speeds, allowing for a visual
survey of the seafloor. This method was only conducted along one survey line when sea
conditions were relatively calm and boat traffic was minimal.
The third method of diver verification was utilized to further investigate areas where seagrass or
hardbottom were observed during the towed video and towboard surveys. Figures 2a-b show the
location of seagrass and hardbottom resources confirmed by diver verification. A CB&I
biologist, accompanied by a field support diver, collected data on the species present, percent
cover, substrate type, and depth, and took representative photographs of the site. When
conditions permitted, divers delineated the resource using a towed buoy equipped with a DGPS
antenna and attached by a cable connected to a topside laptop running HYPACK navigational
software to record the positioning data. A summary of the investigation findings is provided
below.
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Figure 1. Map of the investigation area located in Big Sarasota Pass. The planned field investigation sites and
the towed video and towboard survey lines are shown. A towed video survey line was also conducted along
the depth of closure (DOC) even though it was outside of the investigation area. Labels for each line
correspond to the labeled towed videos provided on the enclosed DVDs.
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RESULTS
Seagrass Resources
Figures 2a-b and Table 1 summarize the seagrass observed during these investigations. No
seagrass resources were observed in the nearshore Lido Key fill placement area. A towed video
survey was also conducted offshore of the fill placement area along the depth of closure (DOC)
(see Figure 1) at approximately 5-6 m (18 ft). No seagrass resources were observed here.
Seagrass resources were observed using the towed video and towboard survey methods in three
main locations within the investigation area: (1) inside Big Sarasota Pass; (2) on the southwest
portion of the Big Sarasota Pass ebb shoal; and (3) offshore of Siesta Key in the southern portion
of the investigation area.
Inside Big Sarasota Pass (Figure 2a), seagrass was present in the northeastern and northwestern
sections of the investigation area and along the seawall located along the north end of Siesta
Key. In the northeastern section a dense patch (Patch 1) of Syringodium filiforme (75-100%
cover) was observed from the vessel and confirmed by diver verification. The patch was
delineated using the diver-towed buoy equipped with a DGPS antenna. The depth was less than 1
m (~2 ft) and the patch extended outside of the investigation area. In the northwestern section of
the Big Sarasota Pass investigation area, several patches of seagrass were observed during the
towboard survey and subsequently confirmed by diver verification. A dense patch (Patch 2) of
Syringodium filiforme (75-100% cover) at approximately 1-2 m (4 ft) depth was observed along
the edge (and continuing outside) of the investigation area and was delineated from the vessel.
Two small patches (Patches 3 and 4) of Halodule wrightii (approximately 50-75% cover) were
observed at a depth of 1.5-2 m (5-6 ft), and fixes were taken at the center of the patches. Three
larger patches (Patches 5, 6, and 7) of H. wrightii were also observed and delineated using the
diver towed buoy. The percent coverage of H. wrightii was greater at Patch 5 (approximately 75100%) than at Patches 6 and 7 (both had approximately 50-75% cover), and depths ranged from
1.5-2 m (5-7 ft). A patch (Patch 8) of S. filiforme was observed along the seawall at the north end
of Siesta Key during the towed video survey and fixes were taken from the vessel (Figure 2b).
This patch was located near the start of the rocky rubble area in approximately 4 m (14 ft) depth.
Due to the strong tidal currents, divers could not safely dive the site to collect in situ data.
Representative photographs of the seagrass resources in Patches 1-8 are presented in Figures 3
through 5.
On the southwest portion of the Big Sarasota Pass ebb shoal, four large patches (Patches 9, 10,
11 and 12) of H. wrightii were observed during the towed video survey and confirmed by diver
verification (Figures 2b and 6). Cover by H. wrightii was sparse, less than 5% at each of the
patches, and depths ranged from 2-3 m (9-11 ft). The substrate consisted mostly of fine sand with
areas of shell hash and dense aggregations of sand dollars (Mellita tenuis). To ensure the areas
surrounding Patches 9-12 were adequately surveyed, intersecting towed video lines were
conducted and fixes were taken to confirm the outer limits of each patch (see lines C1-C7 in
Figure 1).
In the southern portion of the investigation area, located southwest of the north end of Siesta
Key, two small patches (Patches 13 and 14) were observed during the towed video survey and
subsequently confirmed by diver verification (Figures 2b and 7). Fixes were taken at the center
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of each patch. Patch 13 was a sparse patch (few individuals, less than 5% cover) of H. wrightii
that covered approximately 0.5 m2 at 3 m (9 ft) depth. Patch 14 was a dense patch (50-75%
cover) of Halophila decipiens that covered approximately 0.5 m2 at 5 m (17 ft) depth. The
substrate consisted of fine sand and sand dollars at both sites.
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Figure 2a. Location of seagrass patches (Patches 1-7) observed inside Big Sarasota Pass.
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Figure 2b. Location of seagrass patches (Patches 8-14) observed along the seawall on the north end of Siesta
Key, on the southwest portion of the Big Sarasota Pass ebb shoal, and in the southern portion of the
investigation area (offshore of Siesta Key). The location of the rock/rubble resources along the southern
seawall is also shown.
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Table 1. Summary of seagrass observations in the investigation area.
Site
Patch 1
Patch 2
Patch 3
Patch 4
Patch 5
Patch 6
Patch 7
Patch 8
Patch 9
Patch 10
Patch 11
Patch 12
Patch 13
Patch 14
Depth (m)
1
1
2
2
2
2
2
4
3
3
2
3
3
5
Species
Syringodium filiforme
Syringodium filiforme
Halodule wrightii
Halodule wrightii
Halodule wrightii
Halodule wrightii
Halodule wrightii
Syringodium filiforme
Halodule wrightii
Halodule wrightii
Halodule wrightii
Halodule wrightii
Halodule wrightii
Halophila decipiens
Percent Cover
75-100%
75-100%
50-75%
50-75%
75-100%
50-75%
50-75%
*
numerous, but < 5%
numerous, but < 5%
numerous, but < 5%
numerous, but < 5%
few, < 5%
50-75%
*Divers were unable to collect in situ data for Patch 8 due to the unsafe diving conditions at the site.
Patch 1
Patch 2
Patch 3
Patch 4
Figure 3. Photographs of seagrass Patches 1-4 located inside of Big Sarasota Pass. Patches 1 and 2 are S.
filiforme and Patches 3 and 4 are H. wrightii.
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Patch 6
Patch 5
Patch 7
Figure 4. Photographs of seagrass Patches 5-7 located inside of Big Sarasota Pass. All patches consist of H.
wrightii.
Figure 5. Image of Patch 8 recorded during the towed video survey within the channel in Big Sarasota Pass.
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Patch 9
Patch 10
Patch 11
Patch 12
Figure 6. Photographs of seagrass Patches 9-12 located in the southwestern portion of the Big Sarasota Pass
ebb shoal. All patches consisted of H. wrightii.
Patch 13
Patch 14
Figure 7. Photographs of seagrass Patches 13 and 14 located in the southern portion of the investigation area,
offshore of Siesta Key. Patch 13 consists of H. wrightii and Patch 14 is Halophila decipiens.
Hardbottom Resources
Sidescan sonar data provided by the USACE was examined prior to the field survey, and ten
contacts were determined to be potential resources that required further investigation. Also, one
site of potential hardbottom was determined from analysis of aerial images (see Figure 1 hardbottom investigation site). The towed video camera was used to investigate these 11 sites,
four of which resulted in identification of potential resources. All four of these sites (Contacts
19, 20, 22, and 26 in Figure 1) were located along the seawall at the north end of Siesta Key
within Big Sarasota Pass. Towed video camera surveys were conducted along the length of the
channel as well as perpendicular to the shoreline to delineate the edges of benthic resources
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(Figures 1 and 2b). Figure 8 shows representative images of the rock and rubble resources
recorded during the towed video. Diver verification was attempted within the channel and a few
photographs were taken, however due to the strong tidal currents the diving activities were
limited for safety reasons. The benthic resources in this location consisted of large rocks, rubble,
and debris that supported growth of sponges (e.g., Cliona celata, Pione lampa), macroalgae (e.g.,
Caulerpa sp.), and octocorals (e.g., Leptogorgia virgulata) (Figures 8 and 9). Fish species, such
as sheepshead (Archosargus probatocephalus), were also observed utilizing this habitat (Figure
10).
Figure 8. Hardbottom resources located within the channel in Big Sarasota Pass recorded during the towed
video survey. Clockwise from the top: Caulerpa sp., Leptogorgia virgulata, Cliona celata, and Pione lampa.
Figure 9. In situ photographs of the hardbottom resources located within the channel in Big Sarasota Pass.
Clockwise from the top: Caulerpa sp., Leptogorgia virgulata, Cliona celata, and Pione lampa.
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Figure 10. Archosargus probatocephalus (sheepshead) were one of the fish species recorded during the towed
video survey within the channel in Big Sarasota Pass.
LITERATURE CITED
Coastal Planning & Engineering, Inc. (CPE). 1992. Lido Key Beach Nourishment Project,
Environmental Study. Prepared for the City of Sarasota, Florida. April 1992. 32 p. + app.
Dial Cordy and Associates, Inc. 2001. Lido Key Shore Protection Project, Marine Resource
Survey Report (October 2001) for the U.S. Army Corps of Engineers. Jacksonville, Florida. 7 p.
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